Sedimentary Basins In China Research Articles

Evaluating the CO2 geological storage suitability of coal-bearing sedimentary basins in China.

The geological storage of CO2 is potentially one of the most effective methods to reduce the CO2 concentration in the atmosphere. Coalbeds are possibly suitable storage reservoirs, meaning that evaluating the suitability of individual coalbeds and associated engineering and construction is an important step in developing geological CO2 storage. This evaluation requires the development of a reasonable evaluation index system and associated weightings. This paper focuses on coal-bearing basins in China and outlines a technical process whereby the CO2 storage suitability of these basins can be comprehensively evaluated. This study uses an earth system science approach to determine the uncertainties involved in identifying ideal CO2 storage sites, develops an index that outlines the conditions related to the suitability of Chinese coal-bearing basins for geological CO2 storage, and incorporates this index into a hierarchical index system model for geological CO2 storage suitability that allows the comprehensive evaluation of coal-bearing basins and includes 5 aspects, 23 indexes, and 5 index levels. The weighting assigned to each evaluation index was determined using the analytic hierarchy process (AHP) and was subsequently incorporated into a fuzzy logic-based comprehensive evaluation approach. This approach was applied to assess the suitability of the Qinshui Basin for geological CO2 storage, revealing that this basin is indeed a suitable coalbed reservoir. The comprehensive geological CO2 storage evaluation model outlined here can also assess the CO2 storage suitability and capacity of other coal-bearing basins elsewhere in China and globally.

Experimental study of the influences of pressure on generation and expulsion of hydrocarbons: A case study from mudstone source rocks and its geological application in the Tarim Basin

Generally, pressure, temperature, depth of organic matter/kerogen burial and organic and inorganic matter interactions can influence the hydrocarbon generation process. However, different understandings were proposed to interpret the role of pressure in hydrocarbon generation. Meanwhile, previous investigations of the influence of pressure on hydrocarbons generation are mainly focused on fluid pressure (FP), only a few work was involved in the effect of lithostatic stress (LS) due to the limitation of experimental techniques. In this study, simulation experiments were conducted to investigate the influence of pressure, including lithostatic stress (LS) and fluid pressure (FP) on yield and process of hydrocarbon generation by a modified simulation instrument. Two systematic comparative pyrolysis experiments, including pressured experiments with LP range from 27.6 to 179.4 MPa and FP range from 12.0 to 109.2 MPa, and non-pressured experiments with LP for 6.0 MPa and FP range from 2.0 to 5.0 MPa were conducted in hydrous experimental condition. The results show that the peak yields of the expelled oil and the liquid hydrocarbons in pressured experiments and non-pressured experiments are 42.48 mg/g·TOC, 52.00 mg/g·TOC, 70.14 mg/g·TOC, and 72.15 mg/g·TOC, respectively. And Ro, ratio of the expelled oil to eluted oil, the accumulated yield of the expelled oil and liquid hydrocarbons, are lower in pressured experiments than that of non-pressured experiments. However, the accumulated yields of eluted oil and residual oil are higher in pressured experiments than that of non-pressured experiments. Additionally, the expulsion efficiencies of the oil range from 20% to 25%, which are lower in pressured experiments than that of non-pressured experiments near the oil generation-window. In addition, the yields of hydrocarbon gas in pressured experiments are greater compared to the yields in non-pressured experiments at the high maturity stage. Based on the experimental results, hydrocarbon generation process can be divided into three stages. Generally, LS and FP could retard the process of mudstone maturation as well as the generation and expulsion of the liquid hydrocarbons. Hence, the residual liquid hydrocarbons in high-pressure condition can act as another source of natural gas generation in the high maturity stage. The results could help us to properly evaluate hydrocarbon generation potentials of sources rocks at petroleum-producing sedimentary basins in China and elsewhere.

Effect of thermal cycling and hydro‐thermal cycling on physical and mechanical properties of sandstone

AbstractThermal storage of sandstone is widely distributed in sedimentary basins in China with a very high degree of exploitation and utilization, while the low recharge rate is the bottleneck of its sustainable development. A new method is proposed to discover the physical and mechanical behaviors of sandstone after thermal cycling and hydro‐thermal cycling treatments in this study. The stress‐strain curves, strength, failure behavior, acoustic emission (AE), P‐wave velocity, density features, X‐ray, and microscope images of specimens are analyzed in detail to investigate and describe the differences of the sandstone after the two different experimental treatments. The results indicate that multiple thermal cycling and hydro‐thermal cycling have an obvious effect on the compaction stage of sandstone at the temperature of 100°C. Meanwhile, strengths and Young's modulus of specimens after hydro‐thermal cycling treatment decrease with cycling times and the reduce degree is greater than that of the thermal cycling treatment on sandstone. The brittleness of the sandstone decreases as the hydro‐thermal cycling number increases from 0 to 15, and the influence of hydro‐thermal cycling is greater than that of thermal cycling on sandstone. In addition, based on the limited cycling experimental results, the action of the thermal cycling leaded the thermal stress of the crystal to nonuniform, which leaded to micronarrow and sharp cracks in specimens. Furthermore, the action of the hydro‐thermal cycling generated thermal stress and ablation coupling effect, which leaded wider and rounder cracks than that of the specimen under thermal cycling condition. Finally, it indicates that hydro‐thermal cycling has a greater effect than that of the thermal cycling treatment on the physical and mechanical properties of sandstone on the macro‐ and microlevels.

Evaluation of CO2 enhanced oil recovery and CO2 storage potential in oil reservoirs of Bohai Bay Basin, China

The Bohai Bay Basin is the largest petroliferous sedimentary basin in China. This basin is encompassed by the Bohai Sea economic zone where a large volume of CO2 is emitted directly into the atmosphere without any treatment. Meanwhile, most of the oil and gas provinces in this basin are facing the selection of tertiary recovery technologies after the completion of water flooding. CO2 enhanced oil recovery (CO2-EOR) is an optimal choice for achieving both a reduction in CO2 emissions and enhanced (or improved) oil recovery. In this paper, an evaluation of the CO2-EOR and CO2 storage potential was carried out at the reservoir scale, based on an established oil reservoir database from numerous data sources, to provide the basis investigating CO2-EOR site selection and regional CO2 emission reduction in China. Moreover, an assessment scheme for the oil reservoirs in the Bohai Bay Basin was also proposed. The results showed that 613 CO2-EOR candidate oil reservoirs, including 354 miscible CO2-EOR candidate oil reservoirs and 259 immiscible CO2-EOR candidate oil reservoirs were identified by applying the screening methodology to 2,891 oil reservoirs in the Bohai Bay Basin. It was predicted that 683 Mt of additional oil can be produced from the CO2-EOR candidate oil reservoirs, and simultaneously 1,345 Mt of CO2 would be incidentally stored in these candidate oil reservoirs. Furthermore, the most prospective area is the miscible CO2-EOR candidate oil reservoirs in the Shengli oil and gas province, where 140 Mt oil could be produced with the CO2-EOR and the injection and incidental storage of 225 Mt of CO2.

Geothermal effects of salt structures on marine sedimentary basins and implications for hydrocarbon thermal evolution

Evaporitic salt is prevalent in marine sedimentary basins, and many discovered hydrocarbon reservoirs are generally associated with salt structures in the world; accordingly salt structures have attracted much attention from academia and industry during the past decade. The Tarim Basin, located in northwest China, is the largest marine sedimentary basin in China with great hydrocarbon resource potential. Previous studies of salt structures in this basin mainly focused on its strong sealing capacity and structural traps created by salt structures. However, besides its extreme impermeability and low viscosity, rock salt has other unique thermal properties, including a large thermal conductivity as high as 5–6 W/(m K), usually 2–3 times greater than that of other common sedimentary rocks, but a relatively low radiogenic heat production. This strong contrast in thermal properties could change the evolving thermal regime and associated thermal history of the source rocks around salt bodies, but it has not been understood well. Herein based on the theoretical models and interpreted salt-bearing seismic profiles from the Kuqa Foreland Basin, northern Tarim Basin, we use 2D finite element numerical experiments to investigate the impacts of salt structures on the basin geothermal regime and associated hydrocarbon thermal evolution. Our results show that, owing to their high efficiency in heat conduction, the salt rocks would result in obviously positive temperature anomalies (3%–13%) above the salt body and negative temperature anomalies (11%–35%) in the subsalt, enhancing and restraining the thermal maturation of source rocks above and below the salt body, respectively. The amplitude and extent of geothermal effects of salt structures depend on the thermal conductivity, geometry, thickness and burial depth of the salt bodies. The thermally affected area around the salt body can be 2 times the salt radius laterally and 2–3 times the salt thickness vertically. Salt structures in the Kuqa Foreland Basin can prominently cool the subsalt formation temperature and accordingly reduce the thermal maturity (Ro) of Jurassic source rocks as much as 18%, enabling the source rocks to stay in the range of gas generation rather than reaching an over-mature stage as expected previously; this situation is favorable for deep hydrocarbon preservation below salt. Because the salt structures in the west and east Kuqa Foreland Basin show strong differences in their thickness, geometric pattern, burial depth and composition, the thermal effects of salt structures on thermal maturation of subsalt source rocks should differ accordingly, which is supported by the observed temporal-spatial variation of Ro for Jurassic source rocks in this basin. Finally, we propose that the geothermal effects of salt structures will be of great importance in the deep hydrocarbon resources potential assessment and exploration in marine sedimentary basins in China.

Hydrogeochemical characteristics of deep saline aquifers in sedimentary basins in China and implications for CO2 geological storage with emphasis on total dissolved solids (TDS) and water type

AbstractThe hydrogeochemistry of deep saline aquifers in sedimentary basins, in particular total dissolved solids, is one of the key criteria for CO2 storage because CO2 solubility is greatly affected by it. A detailed investigation of total dissolved solids (TDS) and water type of formation water is presented in the paper to assess the suitability of sedimentary basins in China for CO2 sequestration. Deep saline aquifers are divided into three categories based on TDS and water type: fresh‐slightly saline water with TDS less than 10 g/L, semi saline–saline water with TDS ranging from 10 g/L to 50 g/L, and salty water with TDS higher than 50 g/L. The fresh, slightly saline water is dominated by water type of Cl·HCO3‐Na in sedimentary basins in East China. Semi saline‐saline and salty waters are of Cl‐Na type existing in the southeast and mid‐west. TDS limits are suggested for different regions of China to optimize the use of formation water. Solubility of CO2 in formation water with TDS of 1g/L∼260g/L is calculated. Results show it exhibits exponential correlation to water TDS and two sharp inflections are observed at 10 g/L and 50 g/L. For fresh‐slightly saline aquifer, TDS limit is defined as 3 g/L in East China while in West China, 5 g/L is suggested. For formation water with TDS of 10 g/L∼150 g/L, 10 g/L is proposed for the main sedimentary basins in China. For deep saline aquifers with TDS higher than 150 g/L, CO2 storage is not suggested to avoid conflicts with salts mineral resources exploration. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.

A Method for Evaluating the Suitability of CO2 Geological Storage in Deep Saline Aquifers

AbstractThis work established an evaluation index system based on a comprehensive analysis of those factors affecting the suitability of CO2 geological storage. This evaluation index system includes three evaluation index layers of geological safety, storage scale and social economy, nine evaluation index sub‐layers, and 28 evaluation index factors, and adopts the analytic hierarchy process (AHP) and index overlay methods. Taking the Xining Basin in northwest China as an example, we conducted comprehensive analysis of geological conditions and performed quantitative evaluation based on this evaluation index system, which indicates that the Shuangshu depression of the Xining Basin is comparatively suitable for CO2 geological storage. It is suggested that this evaluation index system and the evaluation method proposed in this study are suitable for most continental sedimentary basins in China and should be widely applied.

Simulation and analysis of lithology heterogeneity on CO2 geological sequestration in deep saline aquifer: a case study of the Ordos Basin

A simplified two-dimensional axisymmetric model was established based on a typical continental sedimentary basin in China to simulate the thermal evolution of wellbore and reservoir during the injection of CO2 by taking consideration of lithology heterogeneity of reservoir. By comparing with two simple one-dimensional theory models, the lithology heterogeneity influence on CO2 mass flow rate distribution along depth in the wellbore is identified. Results suggested that the interaction of multiple layers in the heterogeneous reservoir will influence the CO2 mass flow rate distribution along depth in the wellbore so as to impact the corresponding temperature and pressure evolution in the wellbore and reservoir. Layer burial depth (or relative location), porosity, permeability and thickness are all important factors that affect CO2 mass flow rate in wellbore. The variation of CO2 mass flow rate in the wellbore will change the CO2 temperature flowing into each layers through impact the heat extraction from rocks, compressibility of CO2 and potential energy loss, and by varying the CO2 hydrostatic pressure and pressure drop due to friction to determine the CO2 injection pressure. Layer burial depth, porosity, permeability and thickness are all important factors that affect the CO2 mass flow rate distribution in the wellbore. This study may help deepen our understanding of CO2 flow and thermal evolution in the actual heterogeneous reservoir and provide important knowledge supplement for the liquid injection (especially CO2) into underground, such as deep saline aquifer, depleted oil/gas reservoir and coal bed.

Geology, geochemistry and sulphur isotopes of the Hat Han gold–antimony deposit, NE Vietnam

The Song Hien Rift basin is considered as one of the important regions for gold deposits in North East Vietnam. Host rocks of a number gold deposits in the Song Hien Rift basin are mainly in Lower Triassic sedimentary formations. However, there is the Hat Han gold deposit hosted in fined-grained mafic magmatic rocks with similar characteristics as gold deposit hosted in the Triassic sediments. Sulphur isotopic compositions of sulphide are similar to those in carbonaceous shale, suggesting that the sulphur was ‘borrowed’ from sedimentary rocks in filling the rift basin. Gold-bearing sulphides (pyrite and arsenopyrite) are the main form of Au presence in the ore. Gold in pyrite is present as Au+1, and a minor amount of as nanoparticles of native Au (Au0); whereas in arsenopyrite, gold is chemically bound as the octahedral complex AuAs2. Analysis of geology, as well as geochemical and isotopic studies show that the genesis of the Hat Han gold deposit is not related to the Cao Bang mafic magmatism; instead the latter only serves as (ore) host rock. The geochemical results presented above suggest that the gabbro host rock only supplies iron needed for sulphide formation. With regard to ore genesis, the Hat Han gold deposit in the Song Hien rift basin was generated in the similar way as sediment-hosted gold deposit. There are many similar typomorphic features between the Hat Han deposit and Carlin-like deposits in the Nanpanjang sedimentary basin in China.

Re-discussion on the detrital zircon provenance of the lower Yanchang Formation in the southern Ordos Basin

AbstractThe Ordos Basin is the second largest sedimentary basin in China. The Yanchang Formation is the key oilbearing layer in the Ordos Basin. The stratigraphic time interval and the stratigraphic division of the Yanchang Formation has been highly debated with estimates ranging from Middle Triassic to Late Triassic. According to the latest studies on the stratigraphical division of Yanchang Formation, it was considered to be deposited as early as the Middle Triassic. Based on this new understanding, we reexamined the previous studies of the detrital zircons from the lower Yanchang Formation. The detrital zircons from the lower Yanchang Formation were divided into three groups based on their U-Pb ages: Paleozoic, Paleoproterozoic, and Neoarchean. The lack of Neoproterozoic U-Pb ages indicates no input from either the Qinling Orogen or the Qilian Orogen. The two older age groups (Paleoproterozoic, and Neoarchean) are likely derived from the North China Craton basement. The Paleozoic zircons were derived from the Inner Mongolia Paleo-uplift. The lower Yanchang Formation was mainly derived from the Inner Mongolia Paleo-uplift instead of being recycled from the previous sedimentary material from the central-eastern North China Craton as was previously hypothesized.

Potential and Suitability Evaluation of CO2 Geological Storage in Major Sedimentary Basins of China, and the Demonstration Project in Ordos Basin

AbstractFrom 2010 to 2012, the China Geological Survey Center for Hydrogeology and Environmental Geology Survey (CHEGS) carried out the project “Potential evaluation and demonstration project of CO2 Geological Storage in China”. During this project, we developed an evaluation index system and technical methods for the potential and suitability of CO2 geological storage based on China's geological conditions, and evaluated the potential and suitability of the primary basins for CO2 geological storage, in order to draw a series of regional scale maps (at a scale of 1:5000000) and develop an atlas of the main sedimentary basins in China. By using these tools, we delineated many potential targets for CO2 storage. We also built techniques and methods for site selection and the exploration and assessment of CO2 geological storage in deep saline aquifers. Furthermore, through cooperation with the China Shenhua Coal to Liquid and Chemical Co., Ltd., we successfully constructed the first coal‐based demonstration project for CO2 geological storage in deep saline aquifers in the Yijinhuoluo Banner of Ordos in the Inner Mongolia Autonomous Region, which brought about the basic preliminary theories, techniques, and methods of geological CO2 storage in deep saline aquifers under China's geological conditions.

Shale Gas in China: Reality and Dream

China extracted shale gas of 23, 500∼24, 600 m3/d from the Lower Cambrian Qiongzhusi Shale Formation in Weiyuan gas field of Sichuan Basin in 1966. This shale interval, however, was considered less prospective because the Sinian Doushantuo Formation dolomite reservoir was defined as the target layer for drilling at that time. Forty years later, this black shale interval became attractive as triggered by the “Shale Gas Evolution” in North America. In 2005, by learning from shale gas mode of the United States, PetroChina Research Institute of Petroleum Exploration and Development (RIPED) reviewed the existing well data of the region where the Weiyuan and Longchang gas fields and the Changning structure were located within the Southern Sichuan Basin. In order to re-examine the gas shows and geochemical property and to evaluate the gas potential of shale strata within the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation and the Lower Cambrian Qiongzhusi Formation. On that basis, for the entire Sichuan Basin and adjoining regions, PetroChina has carried out a geologic survey on organic-rich shales, drilled shallow shale gas appraisal wells, evaluated the shale gas resource potential, and defined some favorable targets for shale gas exploration and development by 2008. W201, the first shale gas appraisal well of China, drilled by PetroChina in 2009, initially produced 17, 000 m3/day from the Wufeng-Longmaxi Formation shale and 10, 800 m3/day from the Qiongzhusi Formation shale, marking the commencement of shale gas exploration and development activities in China. Thus far, China has received shale gas flow from marine, transitional-limnetic coaly and lacustrine shales in many regions, such as Sichuan, Chongqing, Guizhou, etc. The commercialization of marine shale gas has been achieved in Sichuan and Chongqing totaling 0.2 billion cubic meters of shale gas production in 2013. Through an overall review on the progress of shale gas exploration and development in China, we concluded that the geological conditions for shale gas in China are extremely complex. First, the most sedimentary basins in China belong to superimposed basins, all of them have experienced the depositional evolution from marine to terrestrial facies, and three types of shales were well developed including marine, transitional, and terrestrial organic-rich shales. Second, the conditions of shale gas formation and accumulation in China are favorable and shale gas resource has a great potential for further development in China. Third, like North America, the marine organic-rich shales of China have the best and most realistic shale gas exploration and development prospects. But it faces technical, environmental, regulatory, infrastructural and other challenges that are likely to delay rapid shale gas development. Fourth, until now, although the exploration and exploitation of shale gas in China are relatively low, very good signs have been emerged to prove that China has good prospects in the future.

Hydrous pyrolysis maturation of vitrinite-like and humic vitrinite macerals: Implications for thermal maturity analysis

The evaluation of thermal maturity of Lower Paleozoic sedimentary rocks is somewhat complex, mainly because of the absence of humic vitrinite maceral material. Various sedimentary basins of this age contain a syndepositional vitrinite-like maceral that resembles vitrinite but has a lower reflectance. Samples of shales from outcrops and boreholes from the Ponta Grossa Formation (Middle Devonian or older) in the Paraná Basin were studied for maturation assessment. Hydrous pyrolysis assays were conducted for 27 combinations of time and temperature to compare the reflectances of the vitrinite-like maceral and humic vitrinite in response to increasing temperature and time. This data confirmed that the maturation pathway of the vitrinite-like maceral is lower than that of humic vitrinite. The Spore Coloration Index for the outcrop samples was also evaluated for natural series studies. The combination of the natural and artificial series led to the development of two-stage linear regression equations that estimate the equivalent vitrinite reflectance values from measured vitrinite-like maceral reflectances. To validate the proposed equations, reported measurements of vitrinite-like maceral reflectances from sedimentary basins in China, North America and Europe were selected from the literature for comparison. The validations showed that the values obtained from the proposed equations correlated well with other maturity parameters.

On fluid–rock chemical interaction in CO2-based geothermal systems

Although fluid–rock chemical interactions are common natural phenomena associated with ore-forming systems in the crust of the Earth, they may find applications in the utilization of geothermal energy. For example, carbon dioxide is currently considered as an alternative geothermal working fluid because of some favorable behaviors of fluid dynamics and heat transfer when compared to water. While the thermal and hydraulic aspects of a CO2-based geothermal system look promising, especially for the CO2-plume geothermal (CPG) system, major uncertainties remain with regard to chemical interactions between fluids and rocks. We have performed reactive transport modeling to study the impact of fluid–rock interactions in CO2-geothermal systems. A great deal of specific and detailed information is required to assess the geochemistry and heat extraction of a CO2-based geothermal system. The present study is not intended to represent any particular site. However, some geological and geothermal conditions and parameters were taken from: (1) the central depression of the Songliao Basin, Northeastern China, which has the highest geothermal gradient and heat flow among sedimentary basins in China, and (2) the Cranfield CO2 sequestration site, Mississippi, USA, which will be used for a research on CO2-based geothermal power development. The objectives of this study are to investigate: (1) mineral dissolution and precipitation pattern, (2) associated porosity changes and effects on fluid and heat transfer, (3) impacts on the fluid flow, reservoir growth and longevity, and (4) CO2 loss rates (sequestration), or figuring tradeoffs between power generation and CO2 mineralization (geological storage).

Genetic Types of the Alkane Gases in Giant Gas Fields with Proven Reserves over 1000×108m3 in China

By the end of 2011, 20 giant gas fields with proven reserves over 1000×108m3 had been discovered in 7 sedimentary basins in China. Based on the molecular and the carbon isotopic compositions of the alkane gases in these gas fields, in combination with the δ13C1-δ13C2-δ13C3 and δ13C1-C1/C2+3 identification diagrams, the origin of the alkane gases in these 20 giant gas fields are discussed: the alkane gases in Sulige, Daniudi, Yulin, Zizhou, Wushenqi, Hechuan, Guang'an, Anyue, Yuanba, Xinchang, Kela2, Dina2, Dongfang1–1and Kelameili giant gas fields are mainly coal-derived; the alkane gases in Tazhong1 and Datianchi giant gas fields are oil-derived; the alkane gases in Tainan giant gas field are bacterial gases; the alkane gases in Jingbian giant gas field are mixed gases mainly composed of coal-derived gases supplemented with a small quantity of oil-derived gases; the alkane gases in Puguang giant gas field are mixed gases mainly composed of oil-derived gases supplemented with a small quantity of coal-derived gases; the alkane gases in Xushen giant gas field are mixed gases mainly composed of abiogenic gases supplemented with a small quantity of coal-derived gases. The study on the genetic types of the alkane gases in these fields is not only of great scientific importance to the gas correlation, gas accumulation research and the optimization of the exploration targets, but also to the acceleration of the Chinese natural gas industry.

The origin of abnormally high benzene in light hydrocarbons associated with the gas from the Kuqa depression in the Tarim Basin, China

The chemical and carbon isotopic compositions of C1–C3 and C6–C7 light hydrocarbons were analyzed in 14 natural gas samples from the Kela 2, Dabei and Dina 2 gas fields in the Kuqa depression of the Tarim Basin. The relative content of light aromatic compounds (benzene and toluene) in C6–C7 light hydrocarbons is very high, with benzene as the main peak in the gas chromatogram. The relative content of aromatic compounds generally amounts to over 30% of the C6–C7 light hydrocarbons, especially in the Kela 2 gas field where light aromatics comprise more than 70% of the C6–C7 light hydrocarbons. Compared with 255 coal derived gas samples in many other sedimentary basins in China, an abnormal distribution of hydrocarbon composition is observed in the study area. In order to investigate this abnormal distribution, light hydrocarbon yields generated from low maturity coals at different pyrolysis temperatures were simulated quantitatively. The results showed that the yield of light aromatic compounds (benzene and toluene) gradually increases with increasing pyrolysis temperature. Furthermore, the relative content of aromatic hydrocarbons generated from coal samples at high temperatures, similar to an instantaneous accumulation mode under geologic conditions, can amount to 90% of C6–C7 light hydrocarbons, while that of aromatic hydrocarbons generated cumulatively at high temperatures, similar to a cumulative accumulation mode in natural geologic bodies, and is no more than 46.6%. These phenomena have not yet been reported in the literature. By combining these data with carbon isotopic data for natural gas components, it is proposed that an abnormal distribution of aromatic hydrocarbons in gases from the Kuqa depression may imply that the Kela 2 gas field was mainly formed by instantaneous gas accumulation, while the Dabei and Dina 2 gas fields were largely formed by cumulative gas accumulations.

Main Controlled Elements for Accumulation of Ultro-Low Permeability Sandstone Oil Reservoir, Zhenjing Oilfield, Ordas Basin

Ordos Basin is the second largest sedimentary basin in China with very rich oil and gas resources. The exploration targets are typical reservoirs of low permeability. To determine the accumulation mechanism of tight sandstone reservoir, thin section, SEM, numerical calculation were used. The result showed that sandstone should be ultro-low permeability reservoirs with the high content feldspar and lithic arkose or feldspathic litharenite. The reservoir became tight while oil filling, buoyant force is too small to overcome the resistance of capillary force. Therefore, overpressure induced by source rock generation is the accumulation drive force.

Accumulation Mechanism of Ultro-Low Permeability Sandstone Reservoir, Huaqing Oilfield, Ordas Basin

Ordos Basin is the second largest sedimentary basin in China with very rich oil and gas resources. The exploration targets are typical reservoirs of low permeability, low pressure and low output. To determine the accumulation mechanism of tight sandstone reservoir, thin section, fluid inclusion, porosity and permeability measurement, numerical calculation were used. The result showed that sandstone became tight while oil filling, buoyant force is too small to overcome the resistance of capillary force. Therefore, overpressure induced by source rock generation is the accumulation drive force.

Mirror symmetry of the crust in the oil/gas region of Shengli, China

The concept of mirror-image symmetry describes the correlation between the bottom of a sedimentary basin and the top of the underlying mantle. The degree of mirror symmetry is analyzed here using thickness data from Mesozoic–Cenozoic sedimentary basins and the Moho depth, with the purpose of investigating the implications for tectonics and exploratory practices in oil/gas-bearing basins. Our attention is focused on different tectonic elements of a multi-scale tectonic partition in the oil/gas region of Shengli, southeast of Bohai Bay, China. By applying standard least-squares analysis methods to both datasets, we obtained the average thickness h of the consolidated crust and the mirror symmetry factor a for every tectonic unit, thereby allowing us to explore the correlation between the bottom depth of a sedimentary basin and the top of the underlying mantle. A detailed analysis of data uncertainties and their potential effects led to small fluctuations of h and a within a narrow band around the mean values of 33.26km and −1.43, respectively; thus, the results can be considered valid if they are constrained by these error bounds. The issues of crust–mantle interaction and the deviation of the crust from isostatic equilibrium are also addressed for their tectonic implications. Other structural parameters related to the deep-rooted crust beneath the tectonic elements that make up the study region, such as the ratio R of the thickness of the consolidated crust to the absolute value of the symmetry factor, the ratio k of the maximum sediment thickness to the maximum uplift of the mantle, and the product kh, are also evaluated for their implications in geophysical prospecting. The symmetry signature of the crust is compared to the symmetry of other sedimentary basins in China and in the world, suggesting symmetry as a feasible prognostic tool in exploration for oil/gas reservoirs. The key result is that those locations where oil/gas reservoirs have been found to date are basins in which the crust–mantle interaction is active and the crust is isostatically compensated. Both of those parameters can be quantitatively constrained. Conversely, oil and gas reserves are poor or nonexistent in regions where the crust–mantle interaction is inactive and the crust is far from isostatic equilibrium. However, an intermediate case between these two extreme scenarios, wherein the crust–mantle interaction is rather moderate but the crust is in a state close to isostasy, cannot be entirely ruled out.

Feasibility of the Combination of CO2 Geological storage and Saline Water Development in Sedimentary Basins of China

Utilization plays a key role in the deployment of CCS in China. CO2 geological storage and utilization (CGSU) shows most charming potential for carbon mitigation in China according to the technology roadmap study of carbon capture, utilization, and storage (CCUS) in China. After a general review and a thorough investigation, the partition of China mainland into three CCUS zones is figured out mainly according to the different types of aquifer systems. Focusing on coal chemical enterprises in the western China (Zone I), a novel CGSU method is proposed in this paper. By CO2 enhanced recovery of deep saline water, a tripartite win system is charming promotion of China western development. The cross point of the developed system is to attract investment on coal chemical industry to use local rich coal resources, to meet great water demand of coal chemical industry in the water shortage of China western region, and to maximum optimize of pressure buildup of CO2 geological storage.